Rainbow Moonstone
Last updated: April 2026
"Rainbow moonstone" is a widely used trade name for white or colorless labradorite (plagioclase feldspar) that shows a blue adularescence or labradorescence. It is NOT orthoclase moonstone. The distinction is critical and easily made on a refractometer: labradorite reads 1.559–1.572; true orthoclase moonstone reads 1.518–1.526. Despite the trade name, this gem is mineralogically identical to labradorite and should be identified as such. It is one of the most commonly misidentified feldspars in consumer jewelry.
Rainbow Moonstone has a specific gravity of 2.70 and a refractive index of 1.559–1.572, with a Mohs hardness of 6.0–6.5. It is biaxial −.
Physical & Optical Properties
Related: Feldspar Varieties
Key Differentiators
- RI 1.559–1.572 — ABOVE true moonstone (1.518–1.526); this single test identifies it
- "Rainbow moonstone" is white labradorite (plagioclase), NOT orthoclase
- Blue labradorescence/adularescence visible as stone is rocked
- Birefringence 0.011 — slightly higher than true moonstone (0.008)
- Triclinic crystal system (labradorite); true moonstone is monoclinic
Common Simulants
- Moonstone (Adularia): True moonstone (orthoclase/adularia feldspar) shows blue adularescence similar to rainbow moonstone. Key difference: rainbow moonstone is white labradorite (RI 1.559–1.572, SG ~2.70) vs orthoclase moonstone (RI 1.518–1.526, SG ~2.57). Refractometer reading clearly separates them.
- Labradorite: Rainbow moonstone is mineralogically white labradorite. Gray to dark labradorite shows multicolor labradorescence (spectral flash); rainbow moonstone has white body with blue-to-spectral adularescent sheen. Similar RI and SG — distinguish by body color and optical effect character.
- Opalescent Chalcedony: Milky or opalescent chalcedony can superficially resemble rainbow moonstone's sheen. SG ~2.60 (lower than rainbow moonstone ~2.70); RI 1.535–1.539 (lower than rainbow moonstone 1.559–1.572). Lacks the 3D floating adularescent glow — any sheen is surface-based. Aggregate structure visible under magnification.
Commonly Confused With
Commonly confused with: Moonstone.
Measurement Guides
Identifying a rainbow moonstone? GemID walks through these tests in order — RI, SG, fluorescence, and more.
Try GemID Free →Studying for the GIA, FGA, or FEEG practical? Rainbow Moonstone is one of the 130 species in GemID’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
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